Based on the panel data of 248 prefecture-level and above cities in China from 2004 to 2016, we measure the haze-governing performance and adopt the spatial difference in differences (SDID) model to empirically investigate the effect and its mechanism of high-speed rail service intensity on the haze-governing performance. The results are as follows. The enhancement of high-speed rail service intensity is conducive to the improvement of local haze-governing performance, but it worsens the haze-governing performance in neighboring regions with a spatial attenuation boundary of 500 km. The enhancement of high-speed railway service intensity improves local haze-governing performance through three transmission channels: industrial structure, technological innovation, and human capital agglomeration effects. However, its enhancement can affect the haze-governing performance in neighboring regions through the spatial correlation effect of the haze-governing performance and the siphon effect of human capital. The improvement of high-speed railway service intensity has a more evident effect on the haze-governing performance in the central and western regions than that in the eastern regions, but its improvement has no significant effect on the haze-governing performance in resource-based cities. Meanwhile, the improvement only has negative spatial spillover effects on the haze-governing performance in the central and western regions.